1085 300CD has 250k miles on it. The vacuum pump produces 29-30 when tested at idle, so it is doing pretty good for producing vacuum. Why should I replace it? I have read that internal parts can break up and that it should be rebuilt at around 200k. After having bought a timing chain replacement kit, I was shocked to find my timing to be perfect, so no need to replace the chain. Any need to rebuild the pump?

You have small bearings that can come apart and jam up in your timing chain.

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Milan Brown 1979 240D, rebuilt OM617.952 turbo diesel, rebuilt 722.315 transmission (my only daily driver)

Instagram: @maximed93

I am at 450k with original timing chain and vacuum pump. Just do regular oil changes and don't worry about it.

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1985 300 TD 448K
1984 300 TD 278K

1983 240D euro 240k
1994 f-250 idi turbo 330K
1986 f-350 IDI
1987 F-350 IDI

1985 JD 1050 4wd
1965 IH 3660

Mercedes does have a suggested maintenance program on these engines. I have no ideal of how far up in overall millage it applies.

Three items that seem to frequently destroy these engines. Are neglected oil cooler lines. Timing chain breaks and vacuum pump parts breaking timing chains. Keeping an eye on if the motor mount is sagging so far the belt is not cutting into the rubber oil cooler line is just one other thing.

At one time replacement engines in decent condition where almost a dime a dozen. Those days are pretty much gone now.

Since 2007 I have pulled off my vacuum 2 times to inspect it.

However, 2 things kill a vacuum pump. One is a failure of the ball bearing/s which is used as a roller (if you have abnormal noise coming from the vacuum pump area stop driving the Car till you pull the vacuum pump of and inspect it).
The other is if the Intermediate Shaft (this is the shaft that the Timer is attached to) bushing/bearing gets worn and there is too much end play.

If your vacuum pump failed due to the Intermediate Shaft bushing/bearing if you install a New Vacuum Pump you can ruin the new vacuum pump.

See post #3 for a picture of the shaft and bushing:
Vacuum Pump Failure, picking up the pieces?

2 Vacuum Pumps destroyed timer Bushing Identified as the problem
http://www.mbca.org/forum/2013-12-29/why-are-these-vacuum-pumps-being-destroyed
What in particular causes vacuum pump failure?

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84 300D, 82 Volvo 244Gl Diesel

You ask the age old question concerning proactive replacement of a part prior to failure. let's face it, vacuum pumps are mechanical and not even a seer or prophet can predict MTBF (mean time between failure).

Since the consequences of a vacuum pump failure could be fatal to the engine, my recommendation is replace it so you can get some sleep. I'm planning on doing the same replacement very shortly. A long block 617 diesel is around $7,000 while even a used 617 engine isn't cheap.

Pay a little now or possibly pay a lot later.

The problem is that if you have not checked the Timer end play for a worn bushing can cause the vacuum pump failure. That could be an expensive education.

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84 300D, 82 Volvo 244Gl Diesel

This is a picture I copied from someone. Showing the old and new roller setups.

Not shown on the even earlier then the "Old" one in the picture the bearing cages were made of plastic. And the plastic cage over time falls apart.

You will have to ask someone if on the newer one there is a bearing inside of the roller or if the roller just rides on the steel shaft.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

Don't know if it was on this forum or not but someone claimed the little snap-ring came off and the pin slid out and caused a vacuum pump failure.
See snap-rig n attached pic.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

The pump you're showing is for a 60x engine. They did get a design revision in the early 90s and yes, they still have a ball bearing, but encased between steel washers to contain carnage if the cage comes apart. Not sure this redesign ever made it to the 61x engines since they were long out of production by the time the redesign made it to the 60x series.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)